cmd/list: fix -retracted flag description

Change-Id: Ia1ab220485af2f38c3ddcd4c5d5bca1b195a33ed
GitHub-Last-Rev: fb99334
GitHub-Pull-Request: #59847
Reviewed-on: https://go-review.googlesource.com/c/go/+/489175
Auto-Submit: Sam Thanawalla <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Sean Liao <[email protected]>
Reviewed-by: Sam Thanawalla <[email protected]>
Reviewed-by: Carlos Amedee <[email protected]>

Author: goto1134

src/cmd/go/alldocs.go

@@ -300,8 +300,8 @@ space-separated version list.
 
 The -retracted flag causes list to report information about retracted
 module versions. When -retracted is used with -f or -json, the Retracted
-field will be set to a string explaining why the version was retracted.
-The string is taken from comments on the retract directive in the
+field explains why the version was retracted.
+The strings are taken from comments on the retract directive in the
 module's go.mod file. When -retracted is used with -versions, retracted
 versions are listed together with unretracted versions. The -retracted
 flag may be used with or without -m.